1. Field of Invention
This invention relates to a method of manufacturing concrete for placement in air not requiring consolidation by using a hydraulic component material as a binder; not using any anti-foaming agent; and adding small amounts of a water-soluble polymer substance and a high-range air-entraining water-reducing agent.
2. Description of Related Art
Concrete is a composite of materials of different specific gravities such as cement, water, aggregates, and admixtures. Consequently, the Japan Society of Civil Engineers has prescribed many principles in the Standard Specifications for Concrete in view of the present engineering level. Thus, in the clause on mixing, it is stipulated that "mixing shall be performed thoroughly until the mixed concrete has become uniform in quality," and, in the clause on transporting and placing, that "they shall be done in a manner that the segregation of the concrete will be minimized," and further that "concrete is liable to show segregation even when transporting with considerable care concretes of suitable mix proportions. When extreme segregation has been recognized during transportation, thorough re-mixing shall be done to obtain a concrete of uniform quality." It is further prescribed that "the concrete placed shall not be moved laterally inside the form", while indicating that this is ". . . because there is a possibility of concrete segregating every time it is handled." In the clause on consolidation, it is prescribed that "internal vibrators shall be used in principle for consolidation of concrete.", that "concrete, after placement, shall quickly be thoroughly consolidated and reach around reinforcing bars and into corners of the form," and also that "at parts difficult for concrete to reach as where reinforcing bars are densely placed, it is necessary for careful consolidation to be done before the workability of the concrete declines."
As is clear from such principles, even with a concrete which has been adequately mixed by a mixer to be of uniform quality, segregation is liable to occur during the processes of transportation, placement, and consolidation, and reinforcing bars placed densely are great obstacles to flow of concrete, thus causing segregation between mortar and aggregates to take place, with aggregate particles repeatedly coming into contact with each other and congregating locally to close off the gaps between reinforcing bars to obstruct flow of concrete.
It is therefore considered important that in concreting, concrete should be thoroughly consolidated carefully using vibrators while paying special attention, and to fill up all corners of the form.
In recent years, superplasticized concrete (see Japan Society of Civil Engineers (a corporate juridical person)--Concrete Library, No. 51, Guide to Placement of Superplasticized Concrete (Draft)), frequently used as a new technology, is designed to take, with the advent of high-range water-reducing agents, advantage of their powerful dispersing action, and thereby to improve workability as fluid concrete through addition of fluidifier (high-range water-reducing agent) to dry-mix concrete without adding water, but even with superplasticized concrete, segregation is liable to occur in case of dense reinforcement, it further being the principle to use vibrators (internal) for consolidation.
The problematic points as mentioned below exist in concrete widely used at present.
An attempt to increase the fluidity of fresh concrete gives rise to a trend for unit water content to be increased, and for strength and durability to be decreased. Further, when only fluidity is high and deformability is not good, segregation is liable to occur in case there are obstacles such as reinforcing bars, and good filling properties cannot be obtained.
In order to overcome these problems, it is considered an important technological objective to be achieved in this field of engineering to develop a concrete, which not only excels in deformability in its fresh state, but also possesses high resistance to segregation, and which, even without using vibrators, can fill up all corners of forms for concrete members of complex configurations, members with high densities of reinforcing bars, and intricate parts of concrete members.